Kay Kathleen M
Department of Plant Biology, Michigan State University, East Lansing 48824, USA.
Evolution. 2006 Mar;60(3):538-52.
Empirical estimates of the relative importance of different barriers to gene flow between recently diverged species are important for understanding processes of speciation. I investigated the factors contributing to reproductive isolation between Costus pulverulentus and C. scaber (Costaceae), two closely related hummingbird-pollinated understory Neotropical herbs. I studied broad-scale geographic isolation, microhabitat isolation, flowering phenology, overlap in pollinator assemblages, floral constancy by pollinators, mechanical floral isolation, pollen-pistil interactions, seed set in interspecific crosses, and postzygotic isolation (hybrid seed germination, greenhouse survival to flowering, and pollen fertility). Aside from substantial geographic isolation, I found evidence for several factors contributing to reproductive isolation in the sympatric portion of their geographic ranges, but the identity and relative strength of these factors varied depending on the direction of potential gene flow. For C. pulverulentus as the maternal parent, mechanical floral isolation was the most important factor, acting as a complete block to interspecific pollen deposition. For C. scaber as the maternal parent, microhabitat isolation, pollinator assemblage, mechanical floral isolation, and postpollination pollen-pistil incompatibility were important. Overall, prezygotic barriers were found to be strong, resulting in 100% reproductive isolation for C. pulverulentus as the maternal parent and 99.0% reproductive isolation for C. scaber as the maternal parent. Some postzygotic isolation also was identified in the F1 generation, increasing total isolation for C. scaber to 99.4%. The results suggest that ecological factors, including habitat use and plant-pollinator interactions, contributed to speciation in this system and evolved before extensive intrinsic postzygotic isolation.
估算不同障碍对最近分化物种间基因流动的相对重要性，对于理解物种形成过程至关重要。我研究了粉状闭鞘姜和粗糙闭鞘姜（闭鞘姜科）这两种新热带地区林下密切相关的、由蜂鸟传粉的草本植物之间导致生殖隔离的因素。我研究了大规模地理隔离、微生境隔离、开花物候、传粉者组合重叠、传粉者的花粉专一性、花的机械隔离、花粉与雌蕊相互作用、种间杂交的结实率以及合子后隔离（杂种种子萌发、温室中存活至开花以及花粉育性）。除了显著的地理隔离外，我发现有证据表明在其地理分布的同域部分有几个因素导致生殖隔离，但这些因素的性质和相对强度因潜在基因流动方向而异。以粉状闭鞘姜作为母本时，花的机械隔离是最重要的因素，它完全阻止了种间花粉沉积。以粗糙闭鞘姜作为母本时，微生境隔离、传粉者组合、花的机械隔离以及授粉后花粉与雌蕊不亲和性都很重要。总体而言，发现合子前障碍很强，以粉状闭鞘姜作为母本时生殖隔离率达100%，以粗糙闭鞘姜作为母本时生殖隔离率为99.0%。在F1代中也发现了一些合子后隔离，使粗糙闭鞘姜的总隔离率增加到99.4%。结果表明，包括栖息地利用和植物 - 传粉者相互作用在内的生态因素促成了该系统中的物种形成，并且在广泛的内在合子后隔离之前就已演化出来。
